The present invention relates to a sealing device used in a piston portion and others for switching and operating a clutch of a speed-change switching apparatus such as an automatic transmission for an automobile, for example.
A conventional sealing device of this kind is provided with a seal lip on inner and outer peripheries of an annular piston member relating to an input of a speed-change switching in an automatic transmission (A/T, CVT, T/F) of an automobile, for example, mainly, a piston which has a function to receive oil pressure to cause it to input and transmit to the clutch.
FIG. 4 is a sectional view of main parts of an automatic transmission using such a conventional sealing device as described above.
In FIG. 4, reference numeral 100 designates a retaining ring having a substantially U-shaped section mounted on a sleeve 101 mounted on a shaft not shown. The portion having a substantially U-shaped section of the retaining ring 100 forms an annular piston insert hole 102. That is, the retaining ring 100 forms a housing having the annular piston insert hole 102.
A piston member 103 which is annular and has a substantially U-shaped section is slidably arranged in the piston insert hole 102, and a multiple-disc clutch 104 is provided on the outer peripheral side at a lower part in the figure of the piston member 103.
A cancel plate 105 mounted on the inner peripheral side of the piston insert hole 102 is provided between the piston member 103 and the multiple-disc clutch 104. The cancel plate 105 is restricted in its axial movement by means of a stopper 106.
A seal lip 112 as a seal member is provided on the outer periphery of the cancel plate 105, and the seal lip 112 is in sealing contact with the inner peripheral surface of a cylindrical portion 103A on the outer peripheral side of the piston member 103.
A plate-like spring 107 as a bias means is provided between the cancel plate 105 and the piston member 103, and the spring 107 biases the piston member 103 in a direction away from the cancel plate 105, that is, upward in the figure.
The piston member 103 comes in contact with a closed surface 102A of the piston insert hole 102 through a rubber-like elastic member 108 and stands still.
A seal lip 109 which slidably comes in sealing contact with the inner and outer peripheral surfaces of the piston insert hole 102 is provided in the inner and outer peripheries of the piston member 103.
In the manner as described, a pressure chamber X and an oil chamber Y are divisibly formed within the piston insert hole 102.
A cylindrical portion on the inner peripheral side having a portion substantially U-shaped section of the retaining ring 100 forming the piston insert hole 102 has a pressure port 110 in communication with the exterior and the pressure chamber X, and a port 111 in communication with the exterior and the oil chamber Y.
In the above-described constitution, working pressure PA exerts on the pressure chamber X through the pressure port 110 of the retaining ring 100. When pressure rises, the piston member 103 moves axially and downward in the figure against the bias force of the spring 107 to push the multiple-disc clutch 104 at the end of the cylindrical portion 103 of the piston member 103, and to transmit power.
On the other hand, oil is supplied to the oil chamber Y through the port 111 of the retaining ring 100 to lower the pressure of the pressure chamber X whereby the piton member 103 is moved axially (upward in the figure) by the bias force of the spring 107, and the end of the cylindrical portion 103A of the piston member 103 is moved away from the multiple-disc clutch 104 to release the transmission of power.
As described above, the piston member 103 is reciprocated axially to turn ON-OFF the multiple-disc clutch 104.
However, in the case of the above-described prior art, the seal lip 109 provided on the inner and outer peripheries of the piston member 103 comprises a mold lip 109A formed from a mold as shown in FIG. 5(a) and a messcut lip 109B formed from a messcut as shown in FIG. 5(b).
Thereby, since the whole sliding surface of the seal lip 109 comes in contact with the inner and outer peripheral surfaces of the piston insert hole 102, friction increases, and the inferior operation of the piston member 103 occurs accordingly.
For this reason, in the above-described prior art, there occurs an inconvenience of the speed change of the automatic transmission (A/T), for example, a great shock during the speed change, and an inferior feeling during the speed change.
Further, the change of a mechanism according to the magnitude of friction has been required.
That is, it is necessary to increase the force of the spring 107 as the bias means for return of the piston member 103. The particulars of the spring 107 need be redesigned.
This results in drawbacks in that the cost increases, and the entire apparatus becomes so large in size that it is not received in a mounting space of the automobile.